Phase modulated pulse recording and reading systems



Allg- 24, 1965 D. c. J. MAGOTTEAUX 3,202,975

PHASE MODULATED PULSE RECORDING AND READING SYSTEMS Filed March 19, 1962 3 Sheets-Sheet' 1 Aug. 24, 1965 PHASE MODULATED PULSE RECORDING AND READING SYSTEMS Filed MaICh 19, 1962 3 Sheets-Sheet'I 2- nvenfor DES/RE C. nl. MAGOTTEAl/X Aug. 24, 1965 D. c. .1. MAGoT-rEAux 3,202,975

PHASE MODULATED PULSE RECORDING AND READING SYSTEMS Filed March 19, 1962 3 Sheets-Sheet 3 L E n L fm u A Inventor DES/RE C././7AG07'7`EAUX By /7 United States Patent M 3,292,975 PHASE MUDULATED PULSE RECRDiN-G AND READMG SYSTEMS Dsir Camille `iosepli lviagotteaux, Antwerp, Eelgiurn, assigner to international Standard Electric Corporation, New York, N33., a corporation of Delaware Filed Mar. 19, 1962, Ser. No. 186,7tl priority, application Netherlands, Mar. 24, l96l,

262,775 6 Claims. (Cl. 34h-174.1)

The present invention relates to a pulse code conversion circuit for use with phase modulation recording and reading apparatus and more particularly to a pulse code conversion circuit for converting a first two-level information waveform (A), varying between a first or (l-level representing a binary 0 and a second or l-level representing a binary 1, into a phase modulated waveform, wherein the level changes in one sense; i.e. from said first level to said secondV level; of said first information waveform, occur in synchronism with the level changes in the same sense of a first synchronizing waveform (B), whereas the level changes in the other sense, i.e. from said second level to said first level, of said first information waveform occur in synchronisrn with the level changes in the same i Claims Vsense of a second synchronizing waveform (B) which yrespective products AB and AB' are derived, and thus at the output of the mixer which produces the sum AB-l-AB. Indeed, considering the above coincidence gates, itV is clear that spurious signals may appear in coincidence with those variations of the information waveforms A and A which are in afsense oppositetothe concurrent variations of the respective waveforms B and Bf.

Obviously such spurious signals will appear at the output of the above mixer. Besides the latter spurious signals, other spurious signals may appear in the resulting phase modulated waveform, generated at the output of the mixer, in coincidence with the variations ofthe information waveforms A and A in the opposite sense relative to the waveforms B and B since theV associated product waveforms AB and AB appearing at the outputsof the Vabove two coincidence gates will then be varying in oppo.

.site senses. Y Y

The above spurious signals may give rise toerrors in the above phase modulated waveform. f

It is therefore an object of the present invention to provide a code conversion circuit of the above type wherein spurious signals are excluded from the phase vmodulatedwaveform generated at the output of the-above logical circuit. Y

It is to be remarked that a codeV conversion circuit which provides a phase modulated waveform without Vspurious signals as defined above, is disclosed in Belgian Patent 494,234; thiscircuit is composed of tubes and includes differentiation means.V Although dilferentiator means `compatibly adapted for use in tube circuitsiare Y -well knownin the art, such differentiator meanscannot to which all of the above objects are ancillary, to provide a`code conversion circuit of the abovetype wherein no -V v ferent points of said logical circuit;

3,202,975 Patented Aug'. 24, 1965 ICC use is made of differentiating means and which is thus equally compatible for use with both tubes and transistors.

The present pulse code conversion circuit is characterized by the fact that it provides the conversion effect of the Boolean function AB-l-AB, without the associated spurious effects, by applying the Boolean function ABD +ABD-l-C wherein C is a first correction waveform which is normally at said first level but which is at said second level during the intervals overlapping said Vlevel changes in one sense of said first information waveform, and wherein D is a second correction waveform which is normally at said second level but which is at said first level during the intervals overlapping said level changes in said other sense'of said first information waveform.

The above mentioned and other `objects and features of the invention will become more apparent and the invention itself will be best understood by referring tothe following description of an embodiment taken in conjunction with the accompanying drawings in which:

FG. 1 represents a reading and recording arrangement;

FIG. 2 shows the logical circuit according to the invention;

FIG. 3 represents different waveforms appearing at dif- FlG. 4 shows a code conversion logical circuit according to the invention, for converting a phase modulated waveform into a two-level waveform of the type defined above;

FlG. 5 represents different waveforms appearing at different points of the code conversion circuit of FIG.' 4.

Principally referring to FIG. l there is shown a reading and a recording arrangement which includes a number of read-write magnetic head coils MH1 5 each having a central tapping and two outer terminals. This arrangement further includes selecting means constituted by a number -of two-input coincidence gates G1 6 which may for instance be arranged in a matrix. The output of each of these gates is connected to thecentral tap of a correspondingly numbered one of the above magnetic'head coils via an emitter follower (not shown); e.g. the output lead of the two-input coincidence gate G1 is connected to v the central tapping of the magnetic head coil MH1 via a not shown emitter follower. The outer terminals of the above magnetic head coils are each connected to the cathode of`a diode rectifier the anode of which isconnected to the output of'a common recording amplierRAl and to the input of a common reading amplifier RAZ.

It should be remarked-that a reading and Writing arrangement wherein the coils of the magnetic heads each have a central tapping and two outer terminals and wherein the centralV tappings are connected to selecting means, whereas the outer terminals are coupled to a reading andwriting amplifier via a diode,`is shown in the Belgian Patent 558,988. In this arrangement there is however not provided a common reading amplifier and a common writing amplifier, and the selecting means ar rather complicated.

The present arrangement further includes a write shift Vregister SR1 whereinV the information waveform, hereinafter called A, which is to be encoded on a magnetic `rnedium, e.g. a magnetic drum, is stored in telegraphic .pulse code form i.e. the information waveform A varies between first and second levels representing binary 0 and 1 respectively. In `order to be able to`record-the information waveform A in phase modulated form, a logic circuit rLC1 is interposed between the output of the above shift register SR1` and theV input of the above recording amplifier RAl. By means of this logical circuit the Waveform fA is converted into-a phase modulated waveform prior to recording. This logical circuit will further be describe in detail below.

,shown in FIG. 3.V

The arrangement further includes a read shiftregister SR2, which may however be eliminated by time sharing of the above shift register SR1, in the usual manner. Register SR2 lis usedto store in telegraphic pulse'code form lthe information read from the above magnetic drum. lt .is clear that the information recorded in phase modulated form, must be converted into a pulse code'type of wavelated waveform into a waveform of the telegraphic pulse code type, and it will further be described in detail below.

When a reading or writing operation is to be executed, it is necessary to select a particular one of the above magnetic heads MH1 5; e.g.` MH1. For this it is sufficient to'activate the output of the two-inputV coincidenceV gate `(G1) coupled to the central tap of the magnetic head coil, since the potenial thus applied to that centralV tap is suicient to bias both of the diodes connected to the outer terminals of the said coil in the conductive sense.V lt .should be remarked thatthe other non-selected'magnetic heads cannot disturb the reading or writing operationV .executed by means of the selected'magnetic head, since variations the waveforms A+B and Al-B are Varying in opposite senses, with a resultant spurious transient in the product.

Considering the above sum waveforms A+B and A'l-B, it may be noted that spurious signals may be prevented from appearing at the outputs of the above mixers by maintaining these outputs at the l-level during the intervals overlapping the changes .of the information waveform from 0 to 1. Therefore it is suicient to mix the signals A,B as well as A,B with a waveform, hereinaftercalled correction waveform C, `which is normally at the G-level but whichk is at the l-level during the said overlapping intervals. n

Considering further the product waveform (A-l-B) (A21-B), it may be noted that spurious signals which arise in time coincidence with the changes of the information waveform from l to 0, may be prevented from appearing at the output, of the associated coincidence gate through which the product is derived, by maintaining the output of that gate at theVO-level during the intervals overlapping these changes'.r Therefore it is suicient to gate the product of waveforms A+B and A'l-B with a waveform, hereinafter called correction waveform D,

which is normally at the l-level but which is at the O-level current flow through the coils constituting these non# `selected heads is blocked, the diodes associated to each of the latter head-s being all biassed in the non conductive .code form in the shift register SR1', into a phase modulated waveform, suitable for recording on a magnetic drum. The above shift register SR1 comprises a series of vbistable devices only the last and last-but-oneof which,

namely B1 and B2, have beenshown in FIG. 2. The 1 .and (l-outputs of the bistable device B2 are respectively Vcoupled to the'l and O-inputs vof the bistable device B1,

via the two-input coincidence gates G7 and G8 which have a common input connection to the output of a source (not shown) which generates the synchronizing pulse waveform B represented in FIG. 3, only the leading edges of which are effective to control the state of device B1.l The Vwaveform A appears at the 0 output of the bistable device B1 whereas the inverse waveform A' appears at the 1-` output of device B1. Both waveforms, A and A', are

It should be remarked 'that the above Boolean function ABD-l-ABD-i-C may be expressed in a number of equivalent forms; eg. (AB;-I-'AB{C)D or l v(A|B"l-C')(A'ijB-FCD the implementation of which yield identical results.

It should be ,notedl that the waveform B is the inverse of the synchronizing waveform B `and'mayV be obtained from the latterfby passing itV through an inverter.V

ALI-1B, Yit should be clear that Yspurious signals might apduring Vthe last-mentioned intervals.

The above correction waveforms C and D may now beY generated in the following manner.

The waveforms appearing at the 0- and 1outputs of the bistable device B2 are called E and E respectively, these waveforms being identical to the waveforms A and A but advanced by onefperiod T of the synchronizing waveform with respect to the latter waveforms. The

waveforms A', E and B are applied tol the inputs of av bistabledevice cannot modify this condition. This bistable device B4 can only be brought to its l-condition by a leading edge Yof the waveform N and it then remains -in this condition until it is broughtfback to the 0-condition bya leadingfedge ofthe synchronizing waveform .but without the disadvantage, as previously stated, of per-`r rnitting the passage of spurious signals. Y VFIG.,3 showing the waveforms A,A', BB", AV-I-B and `pear at the outputs of mixers through which thelatter, Ysums are derived, at timepositionscorresponding to the variationsof the information waveform Afrom Q to 1, Y

if, at these time positions, the waveform Avariesin a tion Waveform A from l to 0, if at the times of these .sense opposite to the sense of variation of thefwaveformV BJAt'the outputof agate'used to derive the product `(A-l-B) (A21-B) further spurious .signals might ap-'f' Vpear in coincidence with theV variations of theinforrna- In this manner, the above correction Waveform C shown Vin FIG. 3 is generated at the 1output of the v bistable `device B4.

Iny an analogous manner the above correction waveform Dis produced at the O-output of the bistable device B3, to the 0- andhl-inputs of which are respectively applied the synchronizingwaveform B and vthe waveform M, appearing at the output of a three-input coinci- 'dence gate G9, `to the inputs of which are applied the waveforms'qA, E' and B'. Y V

The above'obtained correction waveform C is then applied to an input Vof each of two three-input mixers M1 and M2, to the Vother inputs of which are respec- `tively applied the waveforms;A,BV and A,B. The outputs of mixers M1 and M2.are applied to a irst and a second input of a three-input coincidence gate G11, Y the third input of whichis Aconditioned by the above ,correction waveform D. In this manner thephase modulated waveform F, shown inv FIG. 3, without spurious signals, appears at the output of this coincidence'gate nected to one input of a two-input coincidence gate G12 .and` to one input of a two-inputcoincidencegate G13 via an inverter I1. The other inputs of these gates G12 `and G13 are Vconditioned by av so-called recording aui. "thorization signal Arq.V VThus, only when this signal is The output of thev above coincidence gaterG11'is con-k activated mayinformation be transmitted from the shift register SR1 to the selected magnetic head via the logical circuit LC1 and the recording amplifier RA1.

Principally referring to the FIGURES 4 and 5 the logical circuit LCZ will now be described for converting a phase modulated waveform, such as represented by VF in FIG, 5, into a Waveform in telegraphic pulse code form such as represented by A in the same figure.

This other logical circuit includes a monostable device MS to the l-input of which is fed, via a delay unit DU, a synchronizing waveform B shown in FIG. l5. The 1- output of this monostable device conditions rst inputs of two four-input coincidence gates G and G15, second and third inputs of which are conditioned by a so called reading authorization signal Aug and by the above synchronizing waveform B respectively. The fourth input of the gate G11 is further conditioned by the above phase modulated waveform F, while the fourth input of the gate G15 is conditioned by the inverse waveform F The outputs of the gates G14 and G15 are respectively connected to the 0 and l-inputs of the bistable device B5 via the inverters I2 and I3 respectively.

The waveforms F and B have a relative position such as shown in FIG. 5 and the aim of the circuit comprising the delay unit DU and the monostable device MS is to generate a train of sampling pulses each of which overlaps the trailing edge of synchronizing waveform B.

The delay unit DU shifts the synchronizing waveform B over a predetermined time interval so as to produce the waveform G shown in FIG. 5 and the monostable device MS is then triggered in its unstable condition for a microseconds by each leading edge of the above waveform G. In this manner a waveform H is generated at the l-output of this monostable device MS of the form shown in FIG. 5.

When the reading authorization signal has the authorization value equal to 1, the waveforms K and L Shown in FIG. 5 will appear at the outputs of the gates G14 and G15, Whereas the waveforms K' and L will appear at the output of the inverters I2 and I3 respectively.

When applying the waveforms K' and L to the bistable device B5, a waveform A, rising and falling in coincidence with lagging edges of the respective waveforms K and L, will appear at the O-output thereof.

It should be remarked that only when the above reading authorization signal is activated may information be transmitted fromV a selected magnetic head to the shift register SR2 via the logical circuit LC2 and the reading amplifier RAZ.

Due to the mutually exclusive nature of the above reading and recording authorization signals it is obvious that a reading operation will never disturb a recording operation and vice-versa. Y

While the principles of the invention have been described above in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation on the scope of the invention.

I claim:

1. A circuit for converting a pulse code modulated signal into a phase modulated signal comprising:

(a) a source of pulse code modulated signals E,

(b) a source of periodic Vreference timing signals B,

(c) means coupled to said sources for producing a pulse code signal A identical in form to the said signal E but delayed therefrom by one period (T) of the said periodic signal B,

(d) means coupled to said sources for producing signals representative of the application of the Boole-an function AB-l-AB' to the saidsignals A and B, where A and B are the respective inversesof the said signals A and B,

(e) means coupled to said sources and to said iirst- Y named means for performing a predetermined logic -6 operation on the said signals A, B, and E to Yproduce correction gating signals the durations of which overlap the level transitions of said signal A, and

(f) means for gating the said signals representative of the function AB-l-AB under the control of said correction gating-signals. Y

2. A circuit according to claim 1 wherein:

Y (a) the said means for producing the signal A includes a shift register through which the said signal E is advanced in synchronism with the leading edges of the said signals B, and wherein (b) the said correction gating signal producing means includes:

(c) a first bistable device B3 having a O-input conditioned by the leading edge of the said timing signal B' and a O-output representative of the said signal D,

(d) a second bistable device B1 having a O-input conditioned by the leading edge of the said signal B' and a l-output representative of the said signal C,

(e) a rst gating circuit for producing a signal representative of the application of the Boolean function ABE to the signals A, B and E where E' is the inverse of E,

(f) a second gating circuit for producing a signal representative of the application of the Boolean function ABE to the signals A, B and E,

(g) and means connecting the outputs of said first and second gating circuits to the respective l-inputs of said first and second bistable devices.

3. A circuit according to claim 1 wherein the said correction gating signals include:

(a) a first train of pulse signals C, the durations of which overlap the said level transitions of said signal A in a first sense, and

(b) a second train of pulse signals D, the durations of which overlap the said level transitions of said signal A in the sense opposite to said rst sense.

4. A circuit according to claim 3 wherein:

(a) the signals C are applied in an enabling sense to said gating means, and

(b) the said signals D are applied in an inhibitory sense to the said gating means.

5. A circuit according to claim 3 wherein:

(a) the said means for producing signals representative of said function AB|AB' comprises:

(b) a lrst'three-input mixer M1 to the inputs of which are applied the said signals A, B', and C, and

(c) a second three-input mixer to the inputs of which are applied the said signals AB and C,

(d) and wherein the said means for gating comprises (e) a` three-input coincidence gate to the inputs of which are applied the outputs of said first and second three-input mixers, and the said signal D,

(f) a first two-input coincidence gate having inputs coupled to the output of said three-input coincidence gate and a source of recording authorization signals (g) an inverting circuit coupled to the output of said three-input coincidence gate, and

(h) a second two-input coincidence gate having inputs coupled to the outputs of said inventing cir-cuit and to said source of recording authorization signals.

6. A circuit for converting signals recorded in two level phase modulated form to corresponding two level signals in pulse ycode form comprising: Y Y(a) a source of two level periodic reference timing pulse signals B (b) a source of two-level phase modulated signals F having level transitions occurring in predetermined time relation to the leading edges of corresponding ones of said pulses B,

(c) means coupled to said source B for producing corresponding reference timing pulses H which have the same periodsbut shorter durations then said pulses B, and which are timed to occur out of synchronism with the level transitions of said signal F,

afaoasms (d) rst means coupled` o said sources and to said reference-timing-pulse producing means for producing signalsrepresentative of the application of the inverse .of the Boolean function BHF to said signals (e) second means coupled to -said sources and tosaid reference-timing-pulse producing means for produc- Y ing signals representativel of the application of the .inverse of the. Boolean function BHF to the signals B, H, and F, Where F isrthe inverse of the signal F,

and

(f) bistable storage meanshaving opposed inputs conproducing means.

References Cited bythe Examiner -UNITED STATES PATENTS 4/59 'BuhIendorf 240-l74.1

IRVING L.Y SRAGOW, Primm Examiner. 

1. A CIRCUIT FOR CONVERTING A PULSE CODE MODULATED SIGNAL INTO A PHASE MODULATED SIGNAL COMPRISING: (A) A SOURCE OF PULSE CODE MODULATED SIGNALS E, (B) A SOURCE OF PERIODIC REFERENCE TIMING SIGNALS B, (C) MEANS COUPLED TO SAID SOURCES FOR PRODUCING A PULSE CODE SIGNAL A IDENTICAL IN FORM TO THE SAID SIGNAL E BUT DELAYED THEREFROM BY ONE PERIOD (T) OF THE SAID PERIODIC SIGNAL B, (D) MEANS COUPLED TO SAID SOURCES FOR PRODUCING SIGNALS REPRESENTATIVE OF THE APPLICATION OF THE BOOLEAN FUNCTION AB+A''B'' TO THE SAID SIGNALS A AND B, WHERE A'' AND B'' ARE THE RESPECTIVE INVERSES OF THE SAID SIGNALS A AND B, 